Gamma iron oxide-alkali metal ferrate and process of preparation



Patented May 24, 1949 GAMMA IRON OXIDE-ALKALI METAL FER- RATE ANDPROCESS OF PREPARATION Max A. Mosesman, Baytown, Tex., assignor, bymesne assignments, to Standard Oil Development Company, Elizabeth, N.J., a corporation of Delaware No Drawing. Original application December20, 1946, Serial No. 717,582, now Patent No. 2,455,696. Divided and thisapplication June 23, 1948, Serial No. 34,843

Claims. (Cl. 252-474) This invention is directed to a method forpreparing a composition adapted to be used as a catalyst. Moreparticularly, this invention relates to a method for preparing apromoted catalyst for utilization in the hydrogenation of carbon oxides.

This application is a division of U. S. Serial No. 717,582. filedDecember 20, 1946 (now Patent No. 2,455,696).

It is well known to the art to synthesize hydrocarbons and oxygenatedderivatives of hydrocarbons by passing a mixture of carbon monoxide andhydrogen over a suitable catalyst at elevated temperatures andpressures. This reaction is commonly designated as the Fischer- Tropschsynthesis and is usually carried out at temperatures in the range ofabout 450 to 675 F. and pressures in the range of 100 to 500 pounds persquare inch. Such reactions have customarily been carried out in thepresence of catalysts comprising the oxides of metals in group VIII ofthe periodic table such as the oxides of iron, cobalt, and nickel. It isalso known to use such oxides as catalysts either alone or supported onan inert material such as alumina, kieselguhr, and other such supportingagents. It has also been known to add to the active catalytic materialin the catalyst composition a substance usually designated as a promoterwhich exerts a specific efiect on the catalyst activity, selectivity ofthe reactants to useful products, and on the active life of thecatalyst. Catalysts containing promoters in substantially smallquantities often permit consistently high conversion of the reactants todesired products over much longer periods of operation than is possiblewhen using an unpromoted catalyst.

It is the object of the invention to provide a method for preparing animproved catalyst. Another object of the present invention is to devisea method for preparing a catalyst particularly adapted for use in theFischer-Tropsch synthesis. A further object of this invention is toprepare a catalyst that may be utilized in the synthesis of high'yieldsof useful products by the hydrogenation of carbon oxides during longperiods of operation.

The present invention may be described briefly as involving thepreparation of a catalyst comprising a major portion of iron or an ironoxide of forming an alkali metal ferrate by adding 2 to a mixture of FeOHls and an alkali metal hydroxide an oxidizing agent such as bromine,adding the thus formed alkali metal ferrate to the iron or iron oxidecatalyst, intimately mixing the two, drying and pilling the mixture, andheating the mixture at an elevated temperature of about 1000 F. in thepresence of air to ob tain the finished catalyst. Following the heattreatment in the presence of air, the catalyst is.

then reduced at a temperature in the range between 700 and 1600 F.

The alkali metal ferrate promoter, for example. potassium ferrate, to beadded to the catalyst may be prepared in a number of ways. In thepreferred procedure, FB(NO3)3.9H2O is reacted with ammonium hydroxide tocause the precipitation of Fe(0H)a and the ferric hydroxide thus formedis filtered and then slurried with water. The water slurry is admixedwith solid KOH- and to the mixture is added slowly liquid bromine andsolid KOH until the mixture is saturated with respect to the latter. Thereaction mixture should be kept at a temperature below about F. Themixture may then be heated carefully with stirring for about one-halfhour at about 140 F., allowed to cool, and the top layer removed fromthe reaction mixture. The top layer is dried in a vacuum and then washedwith alcohol until substantially free of alkali. The alcohol-washedmaterial is also dried in a vacuum to produce a potassium ferratesubstantially free from contaminating substances.

The purified potassium ferrate is then added to a powdered iron or topowdered oxide of iron such as ferro-ferric oxide or alpha and gammaferric oxides. It is usually desiredthat sufilcient potassium ferrate beadded to the active catalytic material such that the finished catalystwill comprise about 0.2 to 20 weight per cent potassium ferrate based onthe iron or iron oxide employed.

The mixture of potassium ferrate and iron or iron oxide is milled,preferably in the presence of a small amount of alcohol, dried at atemperature of about 230 F. and pilled. The pilled material is thenheated at superatmospheric temperatures in the presence of air to obtainan active catalyst containing promoting quantities of potassium ferrate.

The presence of both potassium bromide and potassium bromate in smallamounts in the finished catalyst is not objectionable since both ofthese substances may have a tendency to promote the activity of the ironoxide catalyst in the hydrocarbon synthesis reaction.

The practice of the present invention will be further illustrated by thefollowing examples:

To an aqueous solution containing 340 parts by weight of Fe(NO3)3.9H2Ois added 90 parts by weight of NH4OH. The precipitated Fe(OH)a isfiltered dry and then slurried with about 100 parts by weight ofdistilled water. To the slurry is added 50 parts by weight of solid KOHand while the suspension is maintained at a temperature be-- low 140 F.,50 parts by weight of liquid bromine and solid KOH are added. Duringthis addition, the materials are added gradually with continualstirring. Sufilcient solid KOH is added to the reaction mixture so thatthe latter is completely saturated with respect to alkali. At thispoint, it is preferable to add an excess of solid KOH to the mixture,for example, 20 parts by weight on excess alkali, before heating themixture with stirring at a temperature of 140 F. for approximatelyone-half hour.

The heated mixture is allowed to cool and the top layer comprisingpotassium ferrate is decanted from the total mixture and dried underPercent KaFeOc 75.0 KB): 20.0 KBrOa .0

To 100 parts by weight of ferro-ferric oxide in finely divided form isadded 5 parts by weight of dried potassium ferrate and a small amount ofalcohol to permit adequate milling. The mixture is then mixed thoroughlyfor about 4 hours by ball milling, dried at about 230 F. and pilled to asize desired for subsequent use in the synthesis process. The pilledmaterial is then heated in free excess air at about 1000 F. for about 4hours and allowed to cool.

The beneficial results to be obtained by using the above-preparedcatalyst, containing 5 parts by weight of potassium ferrate per 100parts by weight of ferro-ferric oxide in the hydrogenation of carbonmonoxide is exemplified by the following data:

The catalyst prepared in accordance with the above Procedure is placedin a reaction chamber and reduced in the presence of hydrogen for 24hours at a temperature of 700 F. and atmospheric pressure. The hydrogenis passed over the catalyst at a rate of 1000 volumes of hydrogen pervolume of catalyst per hour. A synthesis gas mixture comprising one partof hydrogen per part of carbon monoxide is then passed over the catalystat a pressure of 150 pounds per square inch gauge, a temperature of 575and a rate of 200 volumes per volume of catalyst per hour.

This catalyst was employed in the synthesis of hydrocarbons from carbonmonoxide and hydrogen for 1736 hours. Samples of the products wereexamined during each 24 hour period. During the first 508 hours the 00conversion in mole per cent declined from an initial figure of 97.9 to91% while the selectivity ratio of 04 and heavier hydrocarbons producedto total product in mole per cent increased from an initial figure of64% to as much as 78% and after 508 hours operation was 73.1%. Duringthis period of time, the yield tween 36 and 48. During all this time ofopera-- tion, the test data on the hydrocarbons produced in the processshowed the presence of a considerable amount of alpha olefins. Thepresence of alpha olefins is considered to be very beneficial in thatthe alpha olefins are valuable feed stocks for polymerization to highmolecular weight polymers useful as lubricating oils. The ratio of alphato beta olefins produced during the first 508 hours of operation rangedfrom about 4.6 to as high as 4.7 and the sample obtained just previousto the end of the first 508 hour period showed an alpha olefin to betaolefin ratio of 4.8

Up to 998 hours operation the carbon monoxide conversion in mole percent slowly declined from 91 to 82.5 while the selectivity ratio of 04+hydrocarbons to total product in mole per cent remained fairly constant,the data showing a 74.6% selectivity after 998 hours operation with theimproved catalyst of the present invention. The yield of 04+hydrocarbons in cc. per cubic meter oi. hydrogen and carbon monoxideconsumed after 508 hours was and after 998 hours was still 185; somefluctuation oi. yields during this period was observed with as much as228 cc. of 04+ bydrocarbons being produced per cubic meter of hydrogenand carbon monoxide consumed with the greater amount of the data showingthe production to vary between 170 and cc. The amount of water producedduring this period of time was in the range from about 24 to 42 cc. percubic meter consumption of hydrogen and carbon monoxide. The ratio ofalpha to beta olefins declined slightly during the period to below 3.3.

The improved catalyst of the present invention was continued in use witha slight decline in activity and selectivity until after 1088 hours thecatalyst was reduced with hydrogen at 700 F. for 24 hours at 1000v./v./hr. and at atmospheric pressure. After this treatment, thecatalyst was again used in the synthesis of hydrocarbons from hydrogenand carbon monoxide for a total of 1736 hours.

After the treatment subsequent to 1088 hours employment as catalyst themole per cent carbon monoxide conversion was raised to 99.4 while theselectivity ratio of 04+ hydrocarbons to total product was 70.7%. Theyield 01 04+ hydrocarbons after the foregoing treatment showed only 149cc. per cubic meter of hydrogen and carbon monoxide but increased withinthe next 24 hour period to 203 then in a second 24 hour period to 262and remained in the neighborhood of 200 and higher until 1256 hourstotal operation had ensued. The carbon monoxide conversion declined from94 mole per cent after 1256 hours to 90.1-

pounds and a feed rate of 200 v./v./hr. This tem-' perature was raisedafter 628 hours of operation to 585 F. and in the period between 700hours until the end of the run was maintained at 600 F.

While the foregoing run was terminated after 1736 hours, it is believedthat the improved catalyst could have been used for even longer periodssince, subsequent to the run termination, the synthesis gas feed to thereactor was found to contain 17 P. P. M. of sulfur as H2S. More than P.P. M. of sulfur has been found to poison the activity of the catalyst insynthesizing hydrocarbons.

It will be apparent from the foregoing data that the improved catalystof the present invention may be used for periods up to 1000 hours andhigher while yet obtaining substantial conwere obtained in the case ofthe promoted catalyst. For example, the unpromoted catalyst permittedthe production of only 100 cc. of C4 and heavier products per cubicmeter of hydrogen and carbon monoxide consumed. Furthermore, theunpromoted catalyst possessed a very short life and after only 100 hoursof operation the yields of useful products were reduced to 60 cc. of Cdper cubic meter of hydrogen and carbon monoxide consumed requiringtermination of the run.

In another example, 340 parts of Fe(NO3) 3.9H2O was dissolved indistilled H20. A dilute solution of NH4OH was added to the solution toprecipitate Fe(OH)a. This was filtered and to the filtrate a solution of50 parts of solid KOH dissolved in distilled water was added. Themixture was stirred to a smooth paste while controlling the temperature.To the cooled material 50 parts of bromine was added below the surfaceof the solution while stirring vigorously. Solid KOH was then added insmall quantities until saturation was obtained with the KOH being addedto excess. During the addition of the KOH the temperature was maintainedno higher than 41 C.

and at approximately C. The solution was then carefully heated to 60 C.for one-half hour, heat removed and the solution cooled. Afterapproximately 24 hours, the upper half of the material, hereafterreferred to as the upper layer, was removed. The upper layer and thebottom half, referred to as the lower layer, was then evaporated undervacuum at a temperature of 47 C. for two weeks. After this period boththe ferro-ferric oxide which was thoroughly mixed by stirring to form asmooth slurry. The slurry was dried in an oven at 95 C. with aircirculating freely for a period of 48 hours. The temperature was thenraised to about 110 C. and maintained, with the exception of a 12 hourperiod when the temperature rose to about 160 C., for three weeks. Thedried material was pilled into inch pills which were heated for 4 /2hours in-the presence of an oxygen-containing atmosphere at 1000 F.following which the material was allowed to cool in air to atmospherictemperature. The catalyst prepared in the foregoing manner. comprises 2%by weight of KzFe04 and 98% iron oxid and was then employed for thesynthesis of hydrocarbons from carbon monoxide and hydrogen after beingreduced in the presence of hydrogen for 24 hours at a temperature of 700F. and at atmospheric pressure. During the reduction treatment thehydrogen was passed over the catalyst at the rate of 1000 volumes ofhydrogen per volume of catalyst per hour. A synthesis gas mixturecomprising one part of hydrogen per part of carbon monoxide was employedas the feed stock, the conditions of operation being 150 poundspressure, a temperature of 575 F., and a feed rate of 200 volumes offeed per volume of catalyst per hour.

upper layer and the lower layer were removed Per cent F9203 62.5 K2FeO437.5

A weighed amount of material having the above composition was thensuspended in ethyl alcohol to which was added a weighed amount of In thesynthesis of hydrocarbons in the .foregoing manner using the catalyst,it was found that effective yields of C4 and heavier hydrocarbons couldbe obtained, with the improved method of obtaining the catalysts, forover 600 hours. During certain periods'of the operation as much as 307cc. of C4 and heavier hydrocarbons per cubic meter of feed consumed wereobtained. During longer periods, C4 and heavier hydrocarbon yieldsranging from approximately cc. to 237 cc. per cubic meter of feed stockconsumed were obtained.

It is seen, therefore, that the catalyst composition produced inaccordance with my process is greatly superior to a catalyst which hasnot been promoted with potassium ferrate.

While examples of temperature and pressure conditions suitable for usein the practice of the present invention have been given to illustrateits advantages, it will be obvious to workers skilled in the art thattemperatures and pressures over a substantial range may be employed andgood results obtained. It will also be obvious that the promotingmaterial admixed with the iron or iron oxide catalyst may be presentover a substantial range and satisfactory results obtained. It is notintended that the above-cited examples limit the scope of my invention.

The practice of the invention has been illustrated by'the employment ofpotassium ferrate as the alkali metal ferrate in preparing the catalyst.It is within the scope of the invention to use other alkali metals thanpotassium in preparing the catalyst adapted for use in the Fischer-Tropsch synthesis. For example, sodium and lithium ferrate may be usedin lieu of the potassium ferrate. Potassium ferrate, sodium ferrate, andlithium ferrate may be used, preferably in the order given, in preparingthe catalyst. The lithium ferrate will be less desirable to employ thanthe sodium and potassium ferrate but under some circumstances it may bedesirable to use it.

Having fully described and illustrated the practice of the presentinvention, what I wish to claim as new and useful and to secure byLetters Patent is:

1. A method for preparing a catalyst adapted for use ina'Fischer-Tropsch synthesis which consists of the steps of preparing anadmixture of gamma iron oxide and alkali metal ferrate in an amount inthe range between 0.2 and 20% by weight of said gamma iron oxide,vheating said admixture at a superatmospheric temperature of about 1000F. for about 4 hours in the presence of an oxidizing atmosphere, andsubsequently contacting-the admixture with a reducing atmosphere at asuperatmospheric temperature in the range between 700 and 1600 F. forabout 24 hours.

2. A method of producing a catalyst suitable for use in theFischer-Tropsch"synthesis which consists of the steps of forming analkali metal ierrate substantially free from contaminating materials,admixing the alkali metal ferrate with gamma iron oxide in an amount'sufllcient to form an admixture containing between 0.2 and 20% byweight of alkali metal ferrate based on the gamma iron oxide, heatingthe admixturein the presence of an oxidizing atmosphere at asuperatmospheric temperature of about 1000 F. for about 4 hours andsubsequently reducing the heated mass in a reducing atmosphere at asuperatmospheric termperature of about 700 F. for about 24 hours.

- 3. A method in accordance with claim 2 in which the alkali metalferrate is potassium ferrate.

4. A method in accordance with claim 2 in which the alkali metal ferrateis sodium ferrate.

5. A method in accordance with claim 2 in which the alkali metal Ierrateis lithium ferrate.

6. A composition adapted for use as a catalyst in the production ofhydrocarbons and oxygenated hydrocarbons which consists of a mixture ofgamma iron oxide in an amount in the range between and 99.8% by weightand an alkali metal ferrate in an amount in the range between 0.2 and20% by weight which mixture has been contacted with an oxidizingatmosphere at a temperature of about 1000 F. for about 4 hours and thenwith a reducing atmosphere at a temperature in the range between 700 and1600 F. for about 24 hours.

7. A composition in accordance with claim 6 in which the alkali metalferrate is potassium ferrate.

8. A composition in accordance with claim 6 intwhich the alkali metalferrate is lithium ferra e.

9. A composition in accordance with claim 6 in which the alkali metalferrate is sodium ferrate.

10. A composition adapted for use as a catalyst in the production ofhydrocarbons and oxygenated hydrocarbons which consists of a mixture ofapproximately by weight of gamma iron oxide and approximately 5% byweight of potassium ferrate which mixture has been heated in thepresence of air at a temperatur of the order of 1000 F. for about 4hours and then heated in the presence of hydrogen at a tempera- 30 tureof about 700 F. for about 24 hours.

MAX A. MOSESMAN.

No references cited.

